Amrith, P K
Characterization and management of major pathogens associated with grain discolouration disease of rice - Vellayani Department of plant pathology, college of agriculture 2023 - 145p.
MSc
The study entitled “Characterization and management of major pathogens
associated with grain discolouration disease of rice’’ was carried out at College of
Agriculture, Vellayani and Rice Research Station, Moncompu during 2021-2023,
with the objective of isolation, identification and characterization of pathogens
associated with grain discolouration disease of rice, screening for host plant resistance
and evaluation of different management strategies.
A survey was carried out in three important rice growing districts of Kerala,
viz., Alappuzha, Kottayam and Pathanamthitta covering 14 locations under AEU
04-Kuttanad, during 2022-23 to assess the occurrence and incidence of grain
discolouration disease of rice. The panicle infection percent varied from 71.62 to
100, the spikelet infection percent varied from 63.73 to 89.92, grain discolouration
percent varied from 65.25 to 87.12, disease severity varied from 27.52 to 59.23 per
cent, electrical conductivity varied from 0.12 to 1.43 dSm-1
, pH varied from 3.9 to
5.3 among the survey locations. The common insect pests observed were rice bug,
brown plant hopper, yellow stem borer, shield bug, green leaf hopper and grass
hopper.
The common symptoms observed were varying range of brown to black
spots on glumes with brown, black, pale pink or ash grey discolouration of glumes
followed by grain deformation or chaffiness in case of severe infections.
Upon isolation, a total of 42 fungal isolates were obtained which were subcultured and purified. Pathogenicity of these fungal isolates was tested by artificial
inoculation on susceptible rice variety, Uma. Among these, 28 isolates were found
pathogenic.
The studies on cultural and morphological characters of pathogens revealed
that 28 pathogenic isolates mainly belonged to four genera viz., Curvularia,
Bipolaris, Fusarium and Microdochium. Representative virulent isolate(s) from
these four genera were identified and were used for further studies. The two
pathogenic isolates which were unidentified (suspected) based on cultural and
morphological characters were identified through molecular characterization using
ITS primers and the organisms were identified as Microdochium fisheri and
Fusarium moniliforme with accession numbers OR 664110.1 and OR 664027.1
respectively. So total five virulent pathogenic isolates each from Curvularia sp.,
Bipolaris sp., Fusarium sp., Fusarium moniliforme and Microdochium fisheri were
used for further studies.
Seventeen KAU rice varieties for resistance against grain discolouration
disease of rice. The nature of symptoms varied among different varieties. None of
the varieties was found to be immune or resistant. Varieties Shreyas (MO 22) and
Prathyasa (MO 21) were found to be moderately susceptible and rest of varieties
were susceptible or highly susceptible.
In vitro evaluation of biocontrol agents, Bacillus licheniformis (B33) and
Pseudomonas fluorescens (PN026) and three commercial fungicides conducted to
evaluate their efficacy prior to field application revealed that, among the biocontrol
agents, Bacillus licheniformis (B33) inhibited all the five pathogens (57.29 -
66.50%) significantly compared to the control, which was significantly effective
than Pseudomonas fluorescens (PN026) (52.06 – 59.20%). Among the fungicides
evaluated, all the fungicides significantly inhibited the growth of all five pathogens
as compared to the control. Azoxystrobin 18.2% + difenoconazole 11.4 % SC (1000
ppm, 500 ppm and 250 ppm) was significantly effective against Curvularia sp.
(100%, 92.59% and 90.37%) and Microdochium fisheri (100%, 100% and 89.62%),
azoxystrobin 18.2% + difenoconazole 11.4 % SC and copper hydroxide 77 WP
completely inhibited the mycelial growth of Bipolaris sp. at three concentrations,
which were statistically on par. Trifloxystrobin + tebuconazole 50 % 75 WG (400
ppm, 200 ppm and 100 ppm) was completely effective against Fusarium sp. and
Fusarium moniliforme, which was statistically on par.
In vivo evaluation of biocontrol agents and commercial fungicides using
split plot design was carried out during Kharif 2023 at Rice Research Station,
Moncompu. The results revealed that all the treatments significantly reduced the
disease and increased the yield as compared to control. Among the main plot
treatments, as a whole azoxystrobin 18.2% + difenoconazole 11.4 % SC (1ml L-1
)
(foliar spray at booting stage) and among biocontrol agents, Bacillus licheniformis
(B33) (seed treatment (10 g kg-1
), soil application (1 kg acre-1
) at 35 DAP and foliar
spray (20 g L-1
)) was found to be significantly effective than other treatments in
terms of reducing disease severity (16.19%, 32.67%), grain discolouration percent
(14.83, 23.10) and increasing grain yield (7215.83 kg ha-1
, 5949.33 kg ha-1
)
respectively. Among the sub plot treatments, potassium silicate foliar spray @ 5 ml
L
-1 (50 DAP) was significantly effective than lime application in terms of reducing
disease severity (28.92%), grain discolouration percent (25.48) and increasing grain
yield (6274.22 kg ha-1
). In case of interaction effect, as a whole interaction of
Azoxystrobin 18.2% + difenoconazole 11.4 % SC (1ml L-1
) in main plot and
potassium silicate foliar spray @ 5 ml L-1 in sub plot and among biocontrol agent
treatments, Bacillus licheniformis (B33) in main plot and potassium silicate foliar
spray @ 5 ml L-1
in sub plot was significantly effective in terms of reducing disease
severity (14.82%, 30.48%), grain discolouration percent (13.79, 21.57) and
increasing grain yield (7751.67 kg ha-1
, 6445.33 kg ha-1
) respectively.
The results of this study revealed the wide spread occurrence of grain
discolouration disease of rice in major rice growing districts viz., Alappuzha,
Kottayam and Pathanamthitta of Kerala in all the predominant rice varieties. The
major pathogens associated with the disease are identified as Curvularia sp.,
Bipolaris sp., Fusarium sp., Fusarium moniliforme and Microdochium fisheri.
Screening of the rice varieties for resistance revealed none of the varieties were
immune or resistant. As per the study, the biocontrol agent Bacillus licheniformis
(B33) applied as seed treatment (10g kg-1
), soil application (1 kg acre-1
) at 35 DAP
and foliar spray (20 g L-1
) is highly effective in terms of disease management.
Among the fungicides, azoxystrobin 18.2% + difenoconazole 11.4 % SC (1ml L-1
)
followed by trifloxystrobin 25% + tebuconazole 50% 75 WG @ 0.4g L-1
and copper
hydroxide 77 WP @ 2 g L-1
given as foliar spray at booting stage of the crop is
highly effective in terms of disease management. Among the amendments,
potassium silicate applied as foliar spray @5 ml L-1
(50DAP) manages the disease
effectively.
Precise identification of pathogens up to species level, identification of
resistance source and development of effective management strategies using
botanicals, nanotechnology and new generation fungicides need to be explored
English and malayalam
disease of rice
plant pathology
632.3 / AMR/CH PG
Characterization and management of major pathogens associated with grain discolouration disease of rice - Vellayani Department of plant pathology, college of agriculture 2023 - 145p.
MSc
The study entitled “Characterization and management of major pathogens
associated with grain discolouration disease of rice’’ was carried out at College of
Agriculture, Vellayani and Rice Research Station, Moncompu during 2021-2023,
with the objective of isolation, identification and characterization of pathogens
associated with grain discolouration disease of rice, screening for host plant resistance
and evaluation of different management strategies.
A survey was carried out in three important rice growing districts of Kerala,
viz., Alappuzha, Kottayam and Pathanamthitta covering 14 locations under AEU
04-Kuttanad, during 2022-23 to assess the occurrence and incidence of grain
discolouration disease of rice. The panicle infection percent varied from 71.62 to
100, the spikelet infection percent varied from 63.73 to 89.92, grain discolouration
percent varied from 65.25 to 87.12, disease severity varied from 27.52 to 59.23 per
cent, electrical conductivity varied from 0.12 to 1.43 dSm-1
, pH varied from 3.9 to
5.3 among the survey locations. The common insect pests observed were rice bug,
brown plant hopper, yellow stem borer, shield bug, green leaf hopper and grass
hopper.
The common symptoms observed were varying range of brown to black
spots on glumes with brown, black, pale pink or ash grey discolouration of glumes
followed by grain deformation or chaffiness in case of severe infections.
Upon isolation, a total of 42 fungal isolates were obtained which were subcultured and purified. Pathogenicity of these fungal isolates was tested by artificial
inoculation on susceptible rice variety, Uma. Among these, 28 isolates were found
pathogenic.
The studies on cultural and morphological characters of pathogens revealed
that 28 pathogenic isolates mainly belonged to four genera viz., Curvularia,
Bipolaris, Fusarium and Microdochium. Representative virulent isolate(s) from
these four genera were identified and were used for further studies. The two
pathogenic isolates which were unidentified (suspected) based on cultural and
morphological characters were identified through molecular characterization using
ITS primers and the organisms were identified as Microdochium fisheri and
Fusarium moniliforme with accession numbers OR 664110.1 and OR 664027.1
respectively. So total five virulent pathogenic isolates each from Curvularia sp.,
Bipolaris sp., Fusarium sp., Fusarium moniliforme and Microdochium fisheri were
used for further studies.
Seventeen KAU rice varieties for resistance against grain discolouration
disease of rice. The nature of symptoms varied among different varieties. None of
the varieties was found to be immune or resistant. Varieties Shreyas (MO 22) and
Prathyasa (MO 21) were found to be moderately susceptible and rest of varieties
were susceptible or highly susceptible.
In vitro evaluation of biocontrol agents, Bacillus licheniformis (B33) and
Pseudomonas fluorescens (PN026) and three commercial fungicides conducted to
evaluate their efficacy prior to field application revealed that, among the biocontrol
agents, Bacillus licheniformis (B33) inhibited all the five pathogens (57.29 -
66.50%) significantly compared to the control, which was significantly effective
than Pseudomonas fluorescens (PN026) (52.06 – 59.20%). Among the fungicides
evaluated, all the fungicides significantly inhibited the growth of all five pathogens
as compared to the control. Azoxystrobin 18.2% + difenoconazole 11.4 % SC (1000
ppm, 500 ppm and 250 ppm) was significantly effective against Curvularia sp.
(100%, 92.59% and 90.37%) and Microdochium fisheri (100%, 100% and 89.62%),
azoxystrobin 18.2% + difenoconazole 11.4 % SC and copper hydroxide 77 WP
completely inhibited the mycelial growth of Bipolaris sp. at three concentrations,
which were statistically on par. Trifloxystrobin + tebuconazole 50 % 75 WG (400
ppm, 200 ppm and 100 ppm) was completely effective against Fusarium sp. and
Fusarium moniliforme, which was statistically on par.
In vivo evaluation of biocontrol agents and commercial fungicides using
split plot design was carried out during Kharif 2023 at Rice Research Station,
Moncompu. The results revealed that all the treatments significantly reduced the
disease and increased the yield as compared to control. Among the main plot
treatments, as a whole azoxystrobin 18.2% + difenoconazole 11.4 % SC (1ml L-1
)
(foliar spray at booting stage) and among biocontrol agents, Bacillus licheniformis
(B33) (seed treatment (10 g kg-1
), soil application (1 kg acre-1
) at 35 DAP and foliar
spray (20 g L-1
)) was found to be significantly effective than other treatments in
terms of reducing disease severity (16.19%, 32.67%), grain discolouration percent
(14.83, 23.10) and increasing grain yield (7215.83 kg ha-1
, 5949.33 kg ha-1
)
respectively. Among the sub plot treatments, potassium silicate foliar spray @ 5 ml
L
-1 (50 DAP) was significantly effective than lime application in terms of reducing
disease severity (28.92%), grain discolouration percent (25.48) and increasing grain
yield (6274.22 kg ha-1
). In case of interaction effect, as a whole interaction of
Azoxystrobin 18.2% + difenoconazole 11.4 % SC (1ml L-1
) in main plot and
potassium silicate foliar spray @ 5 ml L-1 in sub plot and among biocontrol agent
treatments, Bacillus licheniformis (B33) in main plot and potassium silicate foliar
spray @ 5 ml L-1
in sub plot was significantly effective in terms of reducing disease
severity (14.82%, 30.48%), grain discolouration percent (13.79, 21.57) and
increasing grain yield (7751.67 kg ha-1
, 6445.33 kg ha-1
) respectively.
The results of this study revealed the wide spread occurrence of grain
discolouration disease of rice in major rice growing districts viz., Alappuzha,
Kottayam and Pathanamthitta of Kerala in all the predominant rice varieties. The
major pathogens associated with the disease are identified as Curvularia sp.,
Bipolaris sp., Fusarium sp., Fusarium moniliforme and Microdochium fisheri.
Screening of the rice varieties for resistance revealed none of the varieties were
immune or resistant. As per the study, the biocontrol agent Bacillus licheniformis
(B33) applied as seed treatment (10g kg-1
), soil application (1 kg acre-1
) at 35 DAP
and foliar spray (20 g L-1
) is highly effective in terms of disease management.
Among the fungicides, azoxystrobin 18.2% + difenoconazole 11.4 % SC (1ml L-1
)
followed by trifloxystrobin 25% + tebuconazole 50% 75 WG @ 0.4g L-1
and copper
hydroxide 77 WP @ 2 g L-1
given as foliar spray at booting stage of the crop is
highly effective in terms of disease management. Among the amendments,
potassium silicate applied as foliar spray @5 ml L-1
(50DAP) manages the disease
effectively.
Precise identification of pathogens up to species level, identification of
resistance source and development of effective management strategies using
botanicals, nanotechnology and new generation fungicides need to be explored
English and malayalam
disease of rice
plant pathology
632.3 / AMR/CH PG